1. Field of the Invention
The present invention concerns the testing of Data Transmission Lines and is particularly, but not exclusively, concerned with the testing of telephone lines when used for transmitting data.
2. Description of Related Art
Current line test methods rely on the connection of the line to be tested to a test facility in the exchange or remote multiplexer. The test facility carries out a series of functional and parametric measurements. From these measurements a diagnosis of the status of the line is then attempted, either manually or automatically, by setting parametric thesholds in the test facility. Testing is either `routine`, to confirm the `health` of the line and its termination or `on-demand` in response to a customer complaint. In the latter case the key requirements of the test are to establish that there actually is a problem and, if so, where the problem is. The latter test is necessary in order to discover who is responsible for curing the error. Known test equipment is expensive so the facility it provides is shared over as many lines as possible, there being typically one test unit per exchange.
The main objective when testing a line is to determine whether there are any symptoms of faults which could affect customer service, and if so, whether a service repair is needed. The principal faults are likely to be poor insulation, disconnection of the master socket, or the terminal being not properly connected. The first two would require action by the network operator, while the last is the customer's problem.
With the current trend in network planning towards fewer exchanges, with more remote concentrators and multiplexers and the use of optical fiber transmission, the cost overhead of providing conventional test facilities for the local lines is becoming prohibitive. The smallest multiplexer is the pair gain adaptor, where a number of Plain Ordinary Telephone System (POTS) lines (usually two) are connected to the exchange over a single copper pair, the pair gain adaptor being located close to (or in) the customers' premises. However, the adaptor is still the responsibility of the Network Operator, and the lines to each customer's master socket, the network terminating point (NTP), still need to be tested both routinely and on demand; accordingly a new approach to line testing is needed.